Artem3213212 gave good idea-- detect lexer on opening file, if lexer is not installed, and suggest to install lexer from addons. i was too lazy to implement it. it was idea from 2-3 months ago. now i have tried to make it.
i made new plugin. cuda_lexer_detecter. it will be preinstalled in next Cud.
plugin has database of all lexers in addons. this DB is generated by script from Kvichans.
plugin finds lexer in addons w/o inet connection.
it shows menu to choose lexer if 2+ lexers are ok. and downloads chosen lexer.
it sets lexer after that for opened file. w/o app restart.
it's good.
it was work for evening. not so hard as i thought.